1. Field of the Invention
The present invention generally relates to a flip-chip mount board and a flip-chip mount structure, and particularly relates to a flip-chip mount board provided with a plurality of conductor patterns to which a plurality of bumps provided on an electronic component can be connected via a connection medium provided on the conductor patterns.
2. Description of the Related Art
Recently, there is an improvement in the density of electronic components such as semiconductor chips. Accordingly, finer pitch is required for external connection terminals, such as bumps, provided on electronic components.
Therefore, as for a mount board, it is necessary to provide connection pads at a considerably high density. The mount board, to which the above-described electronic components are to be mounted, is hereinafter referred to as a flip-chip mount board. Also, a high reliability is required when flip-chip mounting the electronic components.
Now, a flip-chip mounting process of an electronic component, e. g., a semiconductor chip, onto a flip-chip mount board will be described. First of all, connection part conductor patterns (hereinafter referred to as conductor patterns) are formed on the flip-chip mount board. Then, the conductor patterns are provided with solder serving as a connection medium. Finally, the flip-chip mounting process is completed by connecting the bumps (e.g., gold bumps) provided on the semiconductor chip to the conductor patterns.
FIGS. 1 and 2 are an enlarged perspective diagram and a plan view, respectively, partially showing a flip-chip mount board 1. As shown in FIGS. 1 and 2, the flip-chip mount board 1 includes a circuit board 2, conductor patterns 3A, 3B, a solder resist 4 and solder lumps 5.
The conductor patterns 3A, 3B are provided on an upper surface of the circuit board 2 so as to form a predetermined pattern. As shown in FIG. 3, a bump 8 made of gold, for example, provided on a semiconductor chip 7 may be connected to a part of the conductor pattern 3A, 3B. Hereinafter, a part of the conductor pattern 3A, 3B, to which part the gold bump 8 is to be connected, will be referred to as a connection pad 9.
Now, the width of the connection pad 9 will be described in detail. As shown in FIG. 2, the conductor pattern 3A, 3B including the connection pad 9 has a uniform width W3 along the whole length. The width W3 is approximately 30 to 60 .mu.m.
Also, the solder resist 4 serving as an insulator is provided over the circuit board 2, except for positions over the conductor patterns 3A, 3B to which positions the semiconductor chip 7 may connected.
In other words, the solder resist 4 is provided with an opening 4a at a position where the semiconductor chip 7 and the conductor patterns 3A, 3b are connected. The gold bumps 8 will be connected to the parts of the conductor patterns 3A, 3B exposed by the opening 4a. Therefore, the remaining parts of the conductor patterns 3A, 3B are covered, and thus protected, by the solder resist 4.
As shown in FIG. 2, the conductor pattern 3A is covered by the solder resist 4 on both ends. The conductor pattern 3B is covered by the solder resist 4 on one end. The other end of the conductor pattern 3B terminates before reaching the solder resist 4.
Generally, in order to mount a semiconductor chip securely on a flip-chip mount board, it is necessary to provide a solder layer having a uniform thickness onto connection pads. In order to achieve a uniform thickness, it is advantageous to increase an area of the connecting pad because the total number of solder particles provided on the connection pad will be also be increased. In other words, unwanted effects due to the variation in the number of solder particles provided on the connection pad can be reduced.
However, when the area of the connection pads is comparatively large, the solder lump 5 may be created when solder particles are coated on the surface of the conductor patterns 3A, 3B with flux, and then fused. This is because a surface tension is produced in the fused solder, which is in a liquid state. The solder lump 5 thus formed on the conductor pattern 3A, 3B has a height H of approximately 20 to 40 .mu.m. The solder lump 5 serves so as to electrically and mechanically connect the gold bump 8 and the conductor pattern 3A, 3B.
It is also noted that with a recent semiconductor chip having a high-density structure, the pitch between the gold bumps is comparatively fine. Thereby, the width of the connection pad, i.e., the conductor pattern, is also reduced.
Accordingly, in order to increase the area of the connection pad while reducing the width thereof, it is necessary to increase the length of the connection pad. In the related art, since the width of the connection pad is equal to the width of the conductor pattern, increasing the length of the connection pad is equivalent to increasing the length of the conductor pattern.
However, when the width of the connection pad, or the conductor pattern is reduced while increasing the length thereof, a uniform solder layer cannot be obtained since solder lumps will be produced at irregular positions. For example, the connection pad has a width of less than 60 .mu.m and a length of more than 300 .mu.m, and it is attempted to form a uniform solder layer having a thickness of approximately 10 to 20 .mu.m. In such case, a uniform solder layer can not be obtained, since, as shown in FIG. 1, the solder lumps 5 will be formed on the conductor patterns 3A, 3B at irregular positions.
Since the solder lumps 5 are provided at irregular positions, positions of the connection pads 9 and positions of the solder lumps 5 will not correspond to each other. Therefore, as shown in FIG. 3, when the semiconductor chip 7 is positioned above the flip-chip mount board 1, the positions of gold bumps 8 and the solder lumps 5 will not correspond to each other.
It is only solder films 6 that are provided at the positions corresponding to the gold bumps 8. FIG. 4 shows a state where the semiconductor chip 7 is mounted on the flip-chip mount board 1. In this state, the solder films 6 do not provide a sufficient joining force between the gold bumps 8 and the connection pads 9. Therefore, there is a need for a mount board which has a higher mounting reliability.